This invention pertains to telecommunications and, more particularly, is concerned with interactive telecommunication systems.
A number of telecommunication systems have been suggested and deployed which allow a terminal user to request particular video information from a remote repository. Services possible with such systems include, but are not limited to, information searches, retrievals, financial transactions, reservations, and shopping.
With some systems, both the user requests and the video information are sent on a single duplex medium such as telephone lines. Examples of such single medium systems are described in U.S. Pat. Nos. 4,500,751 and 4,578,535.
In other systems, requests are sent over telephone lines and the video information is sent over a broader bandwidth medium, such as cable. Examples of such dual media systems are the subjects of U.S. Pat. Nos. 3,746,780 and 4,616,263, and described in I.sup.2 --Elektrotechniek/Elektronica No. 4-1986, pp. 35-39.
With the system of the aforecited U.S. Pat. No. 3,746,780, a user wanting a service telephones a code number to a central facility. At the central facility, the selected video information is recovered from video discs or other storage means and sent as still television frames to the user over cable or other media. As many terminals are usually coupled to the same medium, each still frame contains a location number or address which is read by address detectors located at the terminals. Only those frames with the same address as the terminal are accepted. An accepted frame may be digitally stored by the terminal and repetitively displayed on a conventional television receiver.
Examples of video information include menus, forms, data, text, and still pictures. It is desirable but lacking in the described system to have audio information such as music and voice accompany the video.
In a publication dated May 1978, NHK (the Japan Broadcasting Corporation) a system is described for sending still pictures with accompanying program sound. Frames for a number of programs are time multiplexed. Each video frame has a code identifying the program to which it belongs. The sound signals of all the programs are digitally encoded and time divisionally multiplexed on lines within an audio frame. Both the video and audio frames are in the standard NTSC format. The video frames are sent serially with each video frame followed by two audio frames. Each video frame carries analog video information corresponding to one program, while each audio frame carries digitized audio information corresponding to all programs.
A receiver seizes and records video frames of a selected program for repetitive display. The analog video may be digitized and stored in a solid state memory while apparently the audio is converted to analog and played as received. The NHK system is appropriate for broadcasting a plurality of predetermined programs, but it is not optimal for interactive broadband services where many users can initiate and interact with programs or services at different times.